Antibodies are drawing attention as pharmaceuticals as they are highly stable in plasma (blood) and have few adverse effects. Of them, a number of IgG-type antibody pharmaceuticals are available on the market and many antibody pharmaceuticals are currently under development (Non-patent Documents 1 and 2).
Almost all antibody pharmaceuticals currently available on the market are of the IgG1 subclass. IgG1 type antibodies are expected be useful as anti-cancer antibody pharmaceuticals since they can bind to Fcγ receptor and exert ADCC activity. However, binding of the Fc domain to Fcγ receptor, which is important for effector function such as ADCC, can cause unnecessary adverse effects, and thus it is preferable to eliminate such binding activity from antibody pharmaceuticals intended for neutralizing biological activity (Non-patent Document 3).
Furthermore, since Fcγ receptor is expressed in antigen-presenting cells, molecules that bind to Fcγ receptor tend to be presented as antigens. It has been reported that immunogenicity is and can be enhanced by linking a protein or peptide to the Fc domain of IgG1 (Non-patent Document 4 and Patent Document 1). Interaction between the antibody Fc domain and Fcγ receptor is thought to be a cause of the serious adverse effects encountered in phase-I clinical trials of TGN1412 (Non-patent Document 5). Thus, binding to Fcγ receptor is considered unfavorable in antibody pharmaceuticals intended for neutralizing the biological activity of an antigen from the perspective of adverse effect and immunogenicity.
A method for impairing the binding to Fcγ receptor is to alter the subtype of the IgG antibody from IgG1 to IgG2 or IgG4; however, this method cannot completely inhibit the binding (Non-patent Document 6). One of the methods reported for completely inhibiting the binding to Fcγ receptor is to artificially alter the Fc domain. For example, the effector functions of anti-CD3 antibodies and anti-CD4 antibodies cause adverse effects. Thus, amino acids that are not present in the wild type sequence were introduced into the Fcγ-receptor-binding domain of Fc (Non-patent Documents 3 and 7), and clinical trials are currently being conducted to assess anti-CD3 antibodies that do not bind to Fcγ receptor and anti-CD4 antibodies that have a mutated Fc domain (Non-patent Documents 5 and 8). Alternatively, Fcγ receptor-nonbinding antibodies can be prepared by altering the FcγR-binding domain of IgG1 (at positions 233, 234, 235, 236, 327, 330, and 331 in the EU numbering system) to an IgG2 or IgG4 sequence (Non-patent Document 9 and Patent Document 2). However, these molecules contain novel non-natural peptide sequences of nine to twelve amino acids, which may constitute a T-cell epitope peptide and thus pose immunogenicity risk. There is no previous report on Fcγ receptor-nonbinding antibodies that have overcome these problems.
Meanwhile, physicochemical properties of antibody proteins, in particular, homogeneity and stability, are very crucial in the development of antibody pharmaceuticals. For the IgG2 subtype, heterogeneity originated from disulfide bonds in the hinge region has been reported (Non-patent Document 10 and Patent Document 3). It is not easy to manufacture them as a pharmaceutical in large-scale while maintaining the objective substances/related substances related heterogeneity between productions. Thus, single substances are desirable as much as possible for antibody molecules developed as pharmaceuticals.
IgG2 and IgG4 are unstable under acidic conditions. IgG type antibodies are in general exposed to acidic conditions in the purification process using Protein A and the virus inactivation process. Thus, attention is needed regarding the stability of IgG2 and IgG4 during these processes, and it is preferable that antibody molecules developed as pharmaceuticals are also stable under acidic conditions. Natural IgG2 and IgG4, and Fcγ receptor-nonbinding antibodies derived from IgG2 or IgG4 (Non-patent Documents 6 and 7 and Patent Document 2) have such problems. It is desirable to solve these problems when developing antibodies into pharmaceuticals.
IgG1-type antibodies are relatively stable under acidic conditions, and the degree of heterogeneity originated from disulfide bonds in the hinge region is also lower in this type of antibodies. However, IgG1-type antibodies are reported to undergo non-enzymatic peptide bond cleavage in the hinge region in solutions when they are stored as formulations, and Fab fragments are generated as impurities as a result (Non-patent Document 11). It is desirable to overcome the generation of impurity when developing antibodies into pharmaceuticals.
Furthermore, for heterogeneity of the C-terminal sequence of an antibody, deletion of C-terminal amino acid lysine residue, and amidation of the C-terminal amino group due to deletion of both of the two C-terminal amino acids, glycine and lysine, have been reported (Non-patent Document 12). It is preferable to eliminate such heterogeneity when developing antibodies into pharmaceuticals.
The constant region of an antibody pharmaceutical aimed for neutralizing an antigen preferably has a sequence that overcomes all the problems described above. However, a constant region that meets all the requirements has not been reported.
A preferred form of antibody pharmaceutical administration is thought to be subcutaneous formulation in chronic autoimmune diseases and such. Low-cost, convenient antibody pharmaceuticals that can be administered subcutaneously in longer intervals can be provided by increasing the half-life of an antibody in the plasma to prolong its therapeutic effect and thereby reduce the amount of protein administered, and by conferring the antibody with high stability so that high concentration formulations can be prepared.
In general, it is necessary that subcutaneous formulations are high-concentration formulations. From the perspective of stability or such, the concentration limit of IgG-type antibody formulations is in general thought to be about 100 mg/ml (Non-patent Document 13). Thus, it is a challenge to secure stability at high concentration. However, there is no report published on the improvement of the stability of IgG at high concentrations by introducing amino acid substitutions into its constant region. A method for prolonging the antibody half-life in plasma has been reported and it substitutes amino acids in the constant region (Non-patent Documents 14 and 15); however, introduction of non-natural sequences into the constant region is not unpreferable from the perspective of immunogenicity risk.
As described above, when the purpose of an antibody pharmaceutical is to neutralize an antigen, it is preferable that all the problems described above have been overcome with regard to its constant-region sequence. However, a constant region that meets all the requirements has not been reported. Thus, there are demands for antibody constant regions that have overcome the problems described above.
Documents of related prior arts for the present invention are described below.    [Non-patent Document 1] Janice M Reichert, Clark J Rosensweig, Laura B Faden & Matthew C Dewitz. Monoclonal antibody successes in the clinic. Nature Biotechnology (2005) 23, 1073-1078    [Non-patent Document 2] Pavlou A K, Belsey M J. The therapeutic antibodies market to 2008. Eur. J. Pharm. Biopharm. April 2005; 59(3):389-96    [Non-patent Document 3] Reddy M P, Kinney C A, Chaikin M A, Payne A, Fishman-Lobell J, Tsui P, Dal Monte P R, Doyle M L, Brigham-Burke M R, Anderson D, Reff M, Newman R, Hanna N, Sweet R W, Truneh A. Elimination of Fc receptor-dependent effector functions of a modified IgG4 monoclonal antibody to human CD4. J. Immunol. Feb. 15, 2000; 164(4):1925-33    [Non-patent Document 4] Guyre P M, Graziano R F, Goldstein J, Wallace P K, Morganelli P M, Wardwell K, Howell A L. Increased potency of Fc-receptor-targeted antigens. Cancer Immunol. Immunother. November-December 1997; 45(3-4):146-8    [Non-patent Document 5] Strand V, Kimberly R, Isaacs J D. Biologic therapies in rheumatology: lessons learned, future directions. Nat. Rev. Drug Discov. January 2007; 6(1):75-92    [Non-patent Document 6] Gessner J E, Heiken H, Tamm A, Schmidt R E. The IgG Fc receptor family. Ann. Hematol. June 1998; 76(6):231-48    [Non-patent Document 7] Cole M S, Anasetti C, Tso J Y. Human IgG2 variants of chimeric anti-CD3 are nonmitogenic to T cells. J. Immunol. Oct. 1, 1997; 159(7):3613-21    [Non-patent Document 8] Chau L A, Tso J Y, Melrose J, Madrenas J. HuM291(Nuvion), a humanized Fc receptor-nonbinding antibody against CD3, anergizes peripheral blood T cells as partial agonist of the T cell receptor. Transplantation Apr. 15, 2001; 71(7):941-50    [Non-patent Document 9] Armour K L, Clark M R, Hadley A G, Williamson L M. Recombinant human IgG molecules lacking Fcgamma receptor I binding and monocyte triggering activities. Eur. J. Immunol. August 1999; 29(8):2613-24    [Non-patent Document 10] Chu G C, Chelius D, Xiao G, Khor H K, Coulibaly S, Bondarenko P V. Accumulation of Succinimide in a Recombinant Monoclonal Antibody in Mildly Acidic Buffers Under Elevated Temperatures. Pharm. Res. Mar. 24, 2007; 24(6):1145-56    [Non-patent Document 11] A J Cordoba, B J Shyong, D Breen, R J Harris. Nonenzymatic hinge region fragmentation of antibodies in solution. J. Chromatogr. B. Anal. Technol. Biomed. Life Sci. (2005) 818, 115-121    [Non-patent Document 12] Johnson K A, Paisley-Flango K, Tangarone B S, Porter T J, Rouse J C. Cation exchange-HPLC and mass spectrometry reveal C-terminal amidation of an IgG1 heavy chain. Anal. Biochem. Jan. 1, 2007; 360(1):75-83    [Non-patent Document 13] Shire S J, Shahrokh Z, Liu J. Challenges in the development of high protein concentration formulations. J. Pharm. Sci. June 2004; 93(6):1390-402    [Non-patent Document 14] Hinton P R, Xiong J M, Johlfs M G, Tang M T, Keller S, Tsurushita N. An engineered human IgG1 antibody with longer serum half-life. J. Immunol. Jan. 1, 2006; 176(1):346-56    [Non-patent Document 15] Ghetie V, Popov S, Borvak J, Radu C, Matesoi D, Medesan C, Ober R J, Ward E S. Increasing the serum persistence of an IgG fragment by random mutagenesis. Nat. Biotechnol. July 1997; 15(7):637-40    [Patent Document 1] US 20050261229A1    [Patent Document 2] WO 99/58572    [Patent Document 3] US 2006/0194280